Wood and/or cellulose based products exposed in an outdoor environment are biodegradable, primarily through attack by microorganisms. As a result, they will decay, weaken in strength, and discolor. The microorganisms causing wood deterioration include brown rots such as Postia placenta, Gloeophyllum trabeum and Coniophora puteana, white rots such as Irpex lacteus and Trametes versicolor, dry rots such as Serpula lacrymans and Meruliporia incrassata and soft rots such as Cephalosporium, Acremonium and Chaetomium. Treatment and protection of wood has been practiced for almost as long as the use of wood itself. Some accounts reach back to the beginning of recorded history. For example the Bible in Genesis, 6:13-14 “And God said unto Noah . . . make thee an ark of gopher wood; rooms shall thou make in the ark, and shall pitch it within and without with pitch.” There are also records of wood preservation reaching back to ancient Greece during Alexander the Great's rule, where bridge wood was soaked in olive oil. The Romans also protected their wood by brushing their ship hulls with tar. During the Industrial Revolution wood preservation became a corner stone of the wood processing industry. Inventors and scientists such as Bethell, Boucherie, Burnett and Kyan made historic developments in wood preservation, with the preservative solutions and processes.
For treating the sleepers of the Cologne-Minden railway, one of the first connections between Cologne via Düsseldorf through the Ruhr area, Julius Rütgers founded in 1849 the “Rütgers-werke, being the first impregnation company working with tar oil and carbolineum. Today the use of such compounds is rather limited due to its high content of polycyclic aromatics; nevertheless they are still applied for the preservation of railway sleepers and poles.
Detailed overviews covering the area of wood preservation are provided for example by H. Becker [Seifen Öle Fette Wachse, Vol. 115, 469ff (1989)], and H. Willeitner [Holz als Rohund Werkstoff, 49, 41ff (1991)]
Water is the most common solvent carrier in preservative formulations due to its availability and low cost. For example, between 1984 and 1996 the market for water-borne products has been doubled its volume. Water-borne systems do however have the drawback that they swell timber, leading to increased twisting, splitting and checking than alternatives. For these reason usually organic solvents, for example NMP, white spirit or fatty acid alkyl esters are used. These compounds do not swell the timber, however show various other disadvantages. In particular at least some of these compounds must be regarded as little environmental-friendly due to their toxic potential and high volatility so that they do not match the legal standards which have been introduced by various countries during the recent years. Others, like for example fatty acid alkyl esters can be regarded as ecologically safe, however their solvent power is sometimes poor so that high amounts of carrier are necessary to formulate a preservative composition that is stable over longer storage times and at higher temperatures.
In the context of the present invention reference is made to European patent EP 0453899 B1 (Bayer) disclosing the use of dimethylamides derived from saturated C6-C20 fatty acids as crystallisation inhibitors for azol derivatives which can be applied as fungicides. The patent neither mentions nor suggests the solvent properties of dialkylamides in general nor their use in wood preservation.
The object of the present invention has therefore to provide new compositions for wood or timber preservation avoiding the disadvantages of the state of the art as explained above. In particular the new compositions should exhibit an improved solvent power, comply with the high environmental safety standards and support the biocide activity of standard preservatives.